On the possibility of ventral root fibers undergoing ephaptic excitation under conditions of very severe spinal hyperreflexia

Abstract

Monosynaptic discharges by ventral roots were studied in rats under conditions of pronounced spinal hyperreflexia 5 days after simultaneous transection of the sciatic nerve and spinal cord. In 40% of tests with such rats, an enhanced monosynaptic discharge of a ventral root was found to be followed by a synchronized and high-amplitude discharge similar in shape and amplitude to the response of the ventral root to electrical stimulation of its fibers. The threshold amplitude for elicitation of these extra discharges was close to the amplitude of the ventral root's monosynaptic discharges at which high-amplitude discharges occurred. It is concluded that when the excitability of spinal reflex ares is excessively high, ephaptic transmission of excitation probably occurs in ventral roots from fibers involved in the enhanced reflex discharge to unexcited fibers.